Sec-butylbenzene is useful as a starting material for the production of phenol and methyl ethyl ketone through the steps of air oxidation to the corresponding hydroperoxide followed by cleavage of the hydroperoxide. Phenol can be used as a solvent and in the production of phenol resins, bisphenol A, ε-caprolactam, adipic acid, alkyl phenols, and plasticizers, whereas methyl ethyl ketone can be used as a solvent for lacquers and resins and for dewaxing of lubricating oils.
The conventional route for the production of sec-butylbenzene involves alkylation of benzene with n-butene over a homogeneous catalyst, such as AlCl3 or solid phosphoric acid. The product of the alkylation reaction is a mixture containing mainly sec-butylbenzene (SBB), isobutylbenzene (IBB), tert-butylbenzene, dibutylbenzenes (DSBB), and tributylbenzenes (TSBB). Of these compounds, dibutylbenzenes and tributylbenzenes are separated from the reaction mixture and can then transalkylated into sec-butylbenzene.
However, the boiling points of isobutylbenzene, sec-butylbenzene and tert-butylbenzene are 172.8° C., 173.5° C. and 169° C., respectively, and hence it is difficult to separate these compounds from each other by distillation. Moreover, isobutylbenzene and tert-butylbenzene are known to be inhibitors to the oxidation of sec-butylbenzene to the corresponding hydroperoxide. For example, the rate of oxidation of sec-butylbenzene, when the sec-butylbenzene contains 1% by weight of isobutylbenzene, decreases to about 91% of that when the sec-butylbenzene is free of isobutylbenzene. Similarly, when the isobutylbenzene content is 1.65% by weight, the rate of oxidation decreases to about 86%; when the isobutylbenzene content is 2% by weight, the rate of oxidation decreases to about 84%; and when the isobutylbenzene content is 3.5% by weight, the rate of oxidation decreases to as much as about 82%.
Therefore, in order to ensure the efficiency of the air oxidation step, it is important to minimize the amount of isobutylbenzene and tert-butylbenzene formed as by-products during the alkylation step to produce the sec-butylbenzene.
For example, U.S. Pat. No. 5,059,736 describes a process for producing sec-butylbenzene from benzene and n-butene, comprising reacting benzene and n-butene in the presence of a homogeneous liquid aluminum chloride complex catalyst, said catalyst comprising aluminum chloride, hydrogen chloride, and an aromatic hydrocarbon, wherein the amount of aluminum chloride used as a component of the complex catalyst is from 0.51 to 5% by weight of the benzene used, the reaction temperature is from 20° C. to 70° C., and the amount of isobutylbenzene formed as a by-product is such that the weight ratio of isobutylbenzene to sec-butylbenzene formed is not more than 0.01:1. However, as discussed above, even isobutylbenzene impurities of 1 wt % significantly inhibit the oxidation of sec-butylbenzene to the corresponding hydroperoxide.
U.S. Pat. No. 4,992,606 discloses a process for preparing short chain alkyl aromatic compounds which comprises contacting at least one alkylatable aromatic compound with at least one alkylating agent possessing an aliphatic group having from 1 to 5 carbon atoms under alkylation reaction conditions and in the presence of an alkylation catalyst to provide an alkylated aromatic product possessing at least one alkyl group derived from said alkylating agent, said catalyst comprising a synthetic porous crystalline material known as MCM-22. Similar disclosures are contained in U.S. Pat. Nos. 5,371,310 and 5,557,024 but where the synthetic porous crystalline material is MCM-49 and MCM-56 respectively.
U.S. Pat. No. 5,334,795 discloses a process for the production of ethylbenzene comprising alkylating benzene with ethylene under liquid phase conditions in the presence of a solid, porous acidic alkylation catalyst comprising MCM-22.
International Patent Application No. PCT/US2003/038709, published as WO 2004/052810. discloses a method for alkylating benzene with ethylene in the presence of metal-impregnated MCM-22. The catalysts are selective for mono-ethylbenzene over di- or tri-ethylbenzene.
In an article entitled “Catalytic Properties of Palladium-Zeolite Systems in the Synthesis of Sec-Butylbenzene from Benzene and Ethylene”, Inst Org. Khim. im N. D. Zelinskogo, Moscow, Russia, Neftekhimiya (1994), 34(2), 151-70, Isakov et al. report that various palladium-containing zeolites (HY, cation-exchanged or dealuminated Mn+NaY, H-pentasil) are effective in the alkylation of benzene with ethylene to produce predominantly sec-butylbenzene or sec-butylbenzene. However, the article also reports that the product contains C4-C6 alkenes.
According to the present invention, it has been found that sec-butylbenzene that is substantially free of isobutylbenzene and tert-butylbenzene can be produced in high yield by the alkylation of benzene with ethylene in the presence of catalyst comprising an MCM-22 family zeolite and at least one metal cation selected from Group 10 of the Periodic Table of Elements. Moreover, the alkylation is accompanied by little or no production of ethylene oligomers, such as C4-C6 alkenes.